Pure fluidic devices

ABSTRACT

The two outlet branches of a bistable wall-adhesion amplifier are each connected through a Venturi to a capacitor volume chamber, while the throat of each Venturi is coupled back to that control inlet of the amplifier which when pressurized switches the jet to the other branch. Different triangular-wave outputs are obtainable from the throat of each Venturi, between the throats of the two Venturi&#39;&#39;s, or between the two amplifier branches, the last-mentioned output supplying a square waveform.

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O Umted States Patent 1191 1111 3,717,166 Davies et al. 1451 Feb. 20, 1973 s41 PURE FLUIDIC DEVICES 3,528,442 9/1970 Campagnuolo ..137/81.5 W51 lnvemo're Edward Davies, Pareham; 1232113 11133 fiffriiiif 1:333:133/3112 chrlsmPher Guy 3,576,294 4/1971 Baldwin ..137/s1.5 Cowplam, both Of England 3,605,778 9/1971 Metzger ..137/s1.s 3,628,774 12/1971 Sulich ..137/81.5 X Asslgneel lQ SQXJPLQELL LQ.HIEW WQ E- 3,633,160 1/1972 Paffrath et al. ..137/s1.s x

A.G., Gartenstrasse, Sw1tzerland Primary Examiner-Samuel Scott [22] Filed May 1971 Attorney-Scrivener, Parker, Scrivener & Clarke [21] Appl. No.: 142,165 [30] Foreign Application Priority Data [57] ABSTRACT The two outlet branches of a bistable wall-adhesion May 15,1970 Great Bntam ..23,67l/70 amplifier are each connected through a Venturi to a capacitor volume chamber, while the throat of each [2%] $5.31 venturi is coupled back to that comm] Met of the 6f "ii. 13C 5 amplifier when pressurized switches jet to 1e 0 Searc 7/ the other branch Different triangulabwave outputs are obtainable from the throat of each Venturi, [56] Rem-mus cued between the throats of the two Venturis, or between UNITED STATES PATENTS the two amplifier branches, the last-mentioned output supplymg a square waveform. 3,444,879 5/1969 McLeod, Jr. ..137/81.5 3,429,324 2/ 1969 Brown et al. 4 Claims, 8 Drawing Figures PURE FLUIDIC DEVICES This invention relates to pure fluidic devices and has for an object to provide an improved pure fluidic device which when connected to a source of compressible fluid under pressure is capable of operation as an oscillator.

According to the invention the two outlet branches of a Coanda-type bistable fluidic switch are each connected through a Venturi nozzle to a capacitor chamber, and the throat of the Venturi nozzle in each branch is connected to that control inlet of the Coanda switch which when pressurized tends to switch the output flow to the other outlet branch.

In order that the invention may be more readily understood, an embodiment will now be described in more detail with reference to the accompanying drawings in which:

FIG. 1 is a circuit diagram of one oscillator device according to the invention,

FIG. 2 is a fragmentary diagram illustrating the operation of one of the branches,

FIGS. 3a and 3b show two waveforms respectively obtainable at the throat of the Venturi of FIG. 2 by a positive-change and a negative-change input-pressure step respectively illustrated in FIGS. 30 and 3d,

FIG. 4 shows three different output waveforms A, B, C, available at the throat of the Venturi of FIG. 2 in response to a square-wave input by variation of the position of the throat tapping in the Venturi, and

FIG. 5 shows two pressure waveforms PO, and P0 respectively available at the tappings of the Venturi in each branch of the circuit, and a sawtooth waveform available as the pressure difference between these two tappings, while a square waveform similar to that shown at O in FIG. 4 is available as the pressure difference between the inlet ends of the two Venturis.

Referring now first to FIG. 1, the illustrated oscillator device consists of the following pure fluidic components, which are connected up as shown to form an integrated fluidic circuit. The term integrated fluidic circuit, when used in this specification, is intended to refer to a fluidic circuit all parts of which are formed in a common integral block of material. A bistable Coanda-type fluidic switch 1 has a power inlet 9 for connection to a source of compressible fluid under pressure, and each of its two output branches 7 and 8 is connected via a Venturi 3 to a chamber 4 constituting a fluidic capacitor 4, while the throat of the Venturi 3 in each output branch is connected by a line 10 to that control inlet of the switch 1 which tends to divert the main flow from power inlet 9 to the other outlet branch.

The operation of the circuit will be more readily understood after first examining the characteristics of a Venturi/capacitor series combination subjected to pulsating inputs.

The basic configuration of such a combination is shown in FIG. 2. An input of compressible fluid whose pressure P is subject to variation in rectangular steps; is supplied to the Venturi 3 at 5, and an output P is tapped-off at a position 6 close to the throat of the venturi 3. The waveforms 7 and 8 shown respectively in FIGS. 3a and 3b illustrate the respective outputs obtained from the circuit following a step of change in the pressure P according to whether the step is positive as shown in FIG. 3c or negative as shown in FIG. 3d.

Comparison of the waveforms respectively shown in FIGS. 3a and 3b shows that it is possible to obtain two different time constants r, and T for positive and negative changes of equal magnitude in the applied pressure P so that various output waveforms may be produced by subjecting the circuit to a pulsating signal.

The waveforms shown at A, B and C in FIG. 4 are all obtained in response to a square-wave input pressure P as shown at O, the differences in the waveforms A, B and C being due to variation of the tapping point 6 along the Venturi 3; the action of the Venturi in this combination is to provide a derivative signal in response to a step input. The characteristics described may be utilized to obtain a fluidic oscillator the output waveform of which may be varied as indicated by waveforms A, B and C of FIG. 4. (N.P.) The basic circuit for one form of such an oscillator is described above and illustrated in FIG. 1. This circuit provides a saw-tooth oscillator supplying, as the pressure difference between the Venturi tappings 10 and 11, an extremely well defined saw-tooth waveform, but the same circuit can also be used to provide a square-wave oscillator of extremely well defined waveform by deriving the output from the pressure difference between the two outlets of the Coanda switch I. The output frequency of oscillators employing these techniques is determined by the product RC, in which the value C is defined by the volume of capacitor 4 and the value R is defined by the throat dimensions of the Venturi 3.

The operation of the circuits described is as follows: The circuit of FIG. 1 is unstable due to the positive feedback to the bistable switch 1. Having switched to one of its output branches 7, 8, the power jet coming from inlet 9 will be retained in this position by wall attachment until the flow through this output branch has charged its capacitor reservoir 4 or 5 to a pressure at which the control pressure at the Venturi throat tapping 10 or 11 is sufficient to switch the power jet to the opposite output leg. Similar action will then be repeated on the other output branch, and the periodic operation is self-sustaining. Thus an oscillatory output is produced which is believed to make the oscillator capable of performing at higher pressure ratios than those commonly associated with fluidic devices.

The incorporation of a Venturi in each leg may be said to enable an inductive term to be added to the RC network, thereby producing very positive switching of the bistable device and generating, in the case of a square-wave oscillator, a very clearly defined square waveform. Another advantage of the oscillators according to the invention is that they can be made to function over a wide range of pressure ratios with only a slight shift in basic frequency.

FIG. 5 illustrated three different waveforms D, E AND F, obtainable from the device illustrated in FIG. 1. E and first two waveforms D and E represent the pressures respectively obtained at the tappings l0 and 11 of the two Venturi nozzles 3, while the third waveform F is obtained as the difference between these pressures. A further output of square waveform is obtainable as the difference between the pressures at two tappings I2 and 13 provided respectively at the inlet ends of the two Venturi nozzles 3.

By tapping-off the output signals from static-pressure tappings at suitably chosen points along the Venturi nozzle 3, or in fact chosen in the line of flow between one of the outlet branches of the Coanda-type switch and its associated capacitor receptacle, it is possible to relatively obtain from the device illustrated in FIG. 1 a waveform of accurate square, sawtooth, or triangular output-wave profile, all of which are useful in fluidic frequency-processing and sensing circuits requiring a signal oscillator of some form.

Pulse-width modulation circuits provide an immediate application for a device where an accurate sawtooth or triangular wave profile is a prime requisite.

The apparatus described may be modified within the scope of the invention. Thus though generally preferred, it is not essential for it to be made in one integral block of material.

What we claim is:

1. A pure fluidic oscillator comprising: a Coandatype switch having a power inlet for producing a power jet, a first and a second outlet branch, and a first and a second control inlet respectively associated with each branch and respectively operative when pressurized to cause the power jet to be switched-over to the other branch; a first and a second Venturi nozzle each having an inlet, an outlet and a nozzle passage forming a throat and leading from said inlet through said throat to said outlets, said nozzle passage being provided with a tapping in said throat; and a first and a second capacitor receptacle the first Venturi nozzle having its inlet connected to the first outlet branch of the switch, its outlet connected to the first capacitor receptacle, and its tapping connected to the first control inlet of the switch, and the second Venturi nozzle having its inlet connected to the second outlet branch of the switch, its outlet connected to the second capacity receptacle, and its tapping connected to the second control inlet of the switch, and the oscillator being provided with output connection means that include a connection to a point in the line of flow between one of said outlet branches and its associated capacitor receptacle.

2. An oscillator as claimed in claim 1, which is provided with two output connections respectively subject to the pressure at the tapping of each Venturi nozzle.

3. An oscillator as claimed in claim 1, which is provided with two output connections respectively subject to the pressure at the inlet to each Venturi nozzle.

4. An oscillator as claimed in claim 1, wherein said nozzle passage includes a diffusor portion leading from said throat to the outlet of the nozzle passage. 

1. A pure fluidic oscillator comprising: a Coanda-type switch having a power inlet for producing a power jet, a first and a second outlet branch, and a first and a second control inlet respectively associated with each branch and respectively operative when pressurized to cause the power jet to be switched-over to the other branch; a first and a second Venturi nozzle each having an inlet, an outlet and a nozzle passage forming a throat and leading from said inlet through said throat to said outlets, said nozzle passage being provided with a tapping in said throat; and a first and a second capacitor receptacle the first Venturi nozzle having its inlet connected to the first outlet branch of the switch, its outlet connected to the first capacitor receptacle, and its tapping connected to the first control inlet of the switch, and the second Venturi nozzle having its inlet connected to the second outlet branch of the switch, its outlet connected to the second capacity receptacle, and its tapping connected to the second control inlet of the switch, and the oscillator being provided with output connection means that include a connection to a point in the line of flow between one of said outlet branches and its associated capacitor receptacle.
 1. A pure fluidic oscillator comprising: a Coanda-type switch having a power inlet for producing a power jet, a first and a second outlet branch, and a first and a second control inlet respectively associated with each branch and respectively operative when pressurized to cause the power jet to be switchedover to the other branch; a first and a second Venturi nozzle each having an inlet, an outlet and a nozzle passage forming a throat and leading from said inlet through said throat to said outlets, said nozzle passage being provided with a tapping in said throat; and a first and a second capacitor receptacle the first Venturi nozzle having its inlet connected to the first outlet branch of the switch, its outlet connected to the first capacitor receptacle, and its tapping connected to the first control inlet of the switch, and the second Venturi nozzle having its inlet connected to the second outlet branch of the switch, its outlet connected to the second capacity receptacle, and its tapping connected to the second control inlet of the switch, and the oscillator being provided with output connection means that include a connection to a point in the line of flow between one of said outlet branches and its associated capacitor receptacle.
 2. An oscillator as claimed in claim 1, which is provided with two output connections respectively subject to the pressure at the tapping of each Venturi nozzle.
 3. An oscillator as claimed in claim 1, which is provided with two output connections respectively subject to the pressure at the inlet to each Venturi nozzle. 